1. Field of the Invention
The present invention relates to a position sensing liquid crystal display (PSLCD), and more particularly to a position sensing liquid crystal display and a method for fabricating the same, in which position sensors, such as digitizers, are formed after bonding of upper and lower plates of the liquid crystal display.
2. Discussion of the Related Art
In general, the liquid crystal display at large is provided with an upper plate, a lower plate, and a liquid crystal sealed between the upper plate and the lower plate. The upper plate has a black matrix layer, a common electrode, and color filter layers of R(red), G(green), and B(blue) for displaying colors disposed thereon. The lower plate has data lines and gate lines crossing the other to form a matrix of pixel regions, each having a thin film transistor and a pixel electrode. That is, as shown in FIG. 1, the lower plate 1 is provided with a matrix of thin film transistors, each having a gate electrode gate extended from a scan line, a source electrode S and a drain electrode extended from a data line disposed at fixed intervals. Each of the pixel regions is provided with a pixel electrode 2a having the drain electrode D of the thin film transistor 2 connected thereto. The upper plate 3 is provided with a matrix form of the black matrix layer 4 for blocking transmission of light for parts excluding the pixel electrodes 2a on the lower plate 1. There are R, G, and B color filter layers 5 between the black matrix layer 4, each for displaying a color. A common electrode 6 is formed extended to the color filter layer 5 and the black matrix layer 4. Upon selective application of driving signals to the scanning lines and the data lines from external driving circuits, the liquid crystal display displays an image. Though the aforementioned liquid crystal display has been designed only to display images according to the external driving signals, recently researches are underway in which the liquid crystal display is provided with additional position sensors for efficient use of the display in a notebook computer. That is, if a character or graphic is drawn with a stylus (an electronic pen) on the liquid crystal display equipped with the position sensors, the character or graphic is displayed as drawn.
A related art position sensing liquid crystal display will be explained with reference to the attached drawings. FIG. 2 illustrates a first example of the related art position sensing liquid crystal display.
Referring to FIG. 2, the first example of the related art position sensing liquid crystal display has a digitizer for sensing a position additionally provided outside of a general liquid crystal display independently, i.e., provided with a liquid crystal display 21 and a digitizer panel 23. There is a position sensing layer 23a (hereafter called, "digitizer"), a compensating resistor region 25 around the digitizer 23a for compensating a voltage difference, and signal applying parts 27a, 27b, 27c, and 27d at four corners of the compensating resistor region 25 for applying a position sensing signal. In the aforementioned position sensing liquid crystal display, when the signal applying parts 27a and 27b are applied at a position signal and the signal applying parts 27c and 27d are grounded, the digitizer 23a has a potential distribution from upper side to lower side thereof. When the signal applying parts 27a and 27c are applied at a position signal and the signal applying parts 27b and 27d are grounded, the digitizer 23a has a potential distribution from right side to left side thereof. Thus, when a stylus 29 is brought into contact with a point on the digitizer 23a after selective application of a position sensing signal to the signal applying parts 27a, 27b, 27c, and 27d, a present position of the stylus 29 can be sensed and determined. In the sensing of the position, a voltage of the position of the digitizer 24a at which the stylus 29 is brought into contact is used. The position sensing of even a finger tip touch can be made, which is displayed in turn on a liquid crystal display.
FIG. 3 illustrates a second example of the related art position sensing liquid crystal display. The second PSLCD has a position sensing digitizer provided inside a liquid crystal display panel. As explained in connection with FIG. 1, the second PSLCD is provided with metal, an insulating film, and a semiconductor layer on a glass for displaying an image, wherein a position sensing layer is embodied using the glass of an image data input electrical device. That is, the second PSLCD is provided with an upper plate 21a, a lower plate 21b, and a digitizer 23a between the upper plate 21a and the lower plate 21b. As explained, the upper plate 21a has the black matrix layer (not shown), a color filter layer, and an ITO layer of a common electrode formed thereon. The lower plate 21b has data lines 31, gate lines 33, and pixel electrodes (not shown), and the digitizer 23a has a compensating resistor region 25 around the digitizer and signal applying parts 27b and 27d at four corners of the compensating resistor region 25 (signal applying parts 27a and 27c are not shown).
In the second PSLCD, when the signal applying parts 27a, 27b, 27c and 27d are applied of a position signal, the digitizer 23a exhibits a potential distribution. Accordingly, when stylus 29 is brought into contact with the display, a voltage at the contact point is sensed, thereby allowing to sense the present position. A finger tip touch on the display can be also sensed. Thus, upon a stylus 29 is brought into contact with a position sensing digitizer 23a after selective application of position signal through signal applying parts 27a, 27b, 27c, and 27d, the PSLCD can sense the present position of the stylus 29 by using a capacitive coupling between the digitizer 23a and the stylus 29.
However, the aforementioned related art PSLCD has the following problems. First, the first PSLCD is cumbersome to carry because of the digitizer provided additionally on the outside of the LCD, which makes the LCD thicker and bulkier.
Second, in the case of the second PSLCD, the severe signal interference and the non-uniform potential distribution of a position sensing layer caused by capacitive coupling between the position sensing layer in the digitizer and the common electrode disposed on opposite sides of an insulating film impedes accurate position sensing and degrades the picture quality.
Third, in a case of the first conventional PSLCD, the inaccurate voltage compensation caused by the misaligned digitizer with respect to the panel causes an inaccurate position sensing.